Incidence of stroke, systemic embolism and bleeding events in patients without anticoagulation based on real-world data in Japan: a retrospective cohort study

OBJECTIVES: To examine the incidence of stroke or systemic embolic events (SSEs) and bleeding events in untreated patients with non-valvular atrial fibrillation (NVAF) after widespread use of direct oral anticoagulant agents (DOACs). DESIGN: Multicentre, non-interventional, observational, retrospective cohort study using real-world data in Japan (2016-2018). SETTING: The Mie, Musashino University study of NVAF, which used the Mie-Life Innovation Promotion Center Database. This is a regional clinical database involving one university hospital and eight general hospitals in Mie Prefecture in Japan. PARTICIPANTS: Japanese patients with NVAF (n=7001). PRIMARY AND SECONDARY OUTCOME: The incidence of SSEs and bleeding events. RESULTS: A total of 7001 patients with NAVF were registered, and 53.0% were treated with DOACs, 10.6% were treated with warfarin and 36.4% had no treatment. Additionally, 29.5% of patients with a CHADS2 (congestive heart failure, hypertension, age≥75 years, diabetes, previous stroke or transient ischemic attack) score of 3–6 were untreated. In the no treatment group, the SSE rates by the CHADS2 score (0, 1, 2 and 3–6) were 1.4%, 1.4%, 3.2% and 8.0%, respectively. The rates of bleeding events by the CHADS2 score (0, 1, 2 and 3–6) in the no treatment group were 0.7%, 1.0%, 1.2% and 2.9%, respectively. A multivariate analysis of SSEs in components of the CHADS2 showed that the adjusted HRs were 2.32 for heart failure, 1.66 for an age ≥75 years, 1.81 for diabetes mellitus and 5.84 for prior stroke or transient ischaemic attack. CONCLUSIONS: Approximately one-third of the patients do not receive any anticoagulation in the modern DOAC era in Japan. The SSE rate increases by the CHADS2 score. The SSE rate is low in patients with a CHADS2 score <1, supporting no indication of anticoagulation in current guidelines. In patients with a CHADS2 score >1, the use of anticoagulant drug therapy is recommended because of a higher risk of stroke.